annotate scripts/sparse/spaugment.m @ 20164:df437a52bcaf stable

doc: Update more docstrings to have one sentence summary as first line. Reviewed miscellaneous, sparse, strings in scripts directory. * scripts/miscellaneous/bzip2.m, scripts/miscellaneous/citation.m, scripts/miscellaneous/compare_versions.m, scripts/miscellaneous/computer.m, scripts/miscellaneous/debug.m, scripts/miscellaneous/dir.m, scripts/miscellaneous/edit.m, scripts/miscellaneous/error_ids.m, scripts/miscellaneous/fileattrib.m, scripts/miscellaneous/fullfile.m, scripts/miscellaneous/genvarname.m, scripts/miscellaneous/gzip.m, scripts/miscellaneous/mkoctfile.m, scripts/miscellaneous/news.m, scripts/miscellaneous/open.m, scripts/miscellaneous/parseparams.m, scripts/miscellaneous/recycle.m, scripts/miscellaneous/run.m, scripts/miscellaneous/swapbytes.m, scripts/miscellaneous/tar.m, scripts/miscellaneous/tmpnam.m, scripts/miscellaneous/unpack.m, scripts/miscellaneous/what.m, scripts/sparse/bicg.m, scripts/sparse/bicgstab.m, scripts/sparse/cgs.m, scripts/sparse/colperm.m, scripts/sparse/eigs.m, scripts/sparse/etreeplot.m, scripts/sparse/gmres.m, scripts/sparse/gplot.m, scripts/sparse/ichol.m, scripts/sparse/ilu.m, scripts/sparse/pcg.m, scripts/sparse/pcr.m, scripts/sparse/qmr.m, scripts/sparse/spaugment.m, scripts/sparse/spconvert.m, scripts/sparse/spdiags.m, scripts/sparse/spfun.m, scripts/sparse/spones.m, scripts/sparse/sprandsym.m, scripts/sparse/spstats.m, scripts/sparse/spy.m, scripts/sparse/svds.m, scripts/sparse/treelayout.m, scripts/sparse/treeplot.m, scripts/strings/base2dec.m, scripts/strings/bin2dec.m, scripts/strings/blanks.m, scripts/strings/cstrcat.m, scripts/strings/deblank.m, scripts/strings/dec2base.m, scripts/strings/dec2bin.m, scripts/strings/dec2hex.m, scripts/strings/findstr.m, scripts/strings/hex2dec.m, scripts/strings/index.m, scripts/strings/isletter.m, scripts/strings/isstrprop.m, scripts/strings/mat2str.m, scripts/strings/ostrsplit.m, scripts/strings/regexptranslate.m, scripts/strings/rindex.m, scripts/strings/str2num.m, scripts/strings/strcat.m, scripts/strings/strchr.m, scripts/strings/strjoin.m, scripts/strings/strjust.m, scripts/strings/strmatch.m, scripts/strings/strsplit.m, scripts/strings/strtok.m, scripts/strings/strtrim.m, scripts/strings/strtrunc.m, scripts/strings/substr.m, scripts/strings/untabify.m, scripts/time/datenum.m: Update more docstrings to have one sentence summary as first line.
author Rik <rik@octave.org>
date Mon, 04 May 2015 14:22:02 -0700
parents 9fc020886ae9
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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1 ## Copyright (C) 2008-2015 David Bateman
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2 ##
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3 ## This file is part of Octave.
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4 ##
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5 ## Octave is free software; you can redistribute it and/or modify it
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6 ## under the terms of the GNU General Public License as published by
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7 ## the Free Software Foundation; either version 3 of the License, or (at
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8 ## your option) any later version.
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9 ##
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10 ## Octave is distributed in the hope that it will be useful, but
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 ## General Public License for more details.
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14 ##
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15 ## You should have received a copy of the GNU General Public License
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16 ## along with Octave; see the file COPYING. If not, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {@var{s} =} spaugment (@var{A}, @var{c})
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21 ## Create the augmented matrix of @var{A}.
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22 ##
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23 ## This is given by
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24 ##
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25 ## @example
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26 ## @group
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27 ## [@var{c} * eye(@var{m}, @var{m}), @var{A};
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28 ## @var{A}', zeros(@var{n}, @var{n})]
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29 ## @end group
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30 ## @end example
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31 ##
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32 ## @noindent
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33 ## This is related to the least squares solution of
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34 ## @code{@var{A} \ @var{b}}, by
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35 ##
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36 ## @example
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37 ## @group
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38 ## @var{s} * [ @var{r} / @var{c}; x] = [ @var{b}, zeros(@var{n}, columns(@var{b})) ]
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39 ## @end group
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40 ## @end example
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41 ##
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42 ## @noindent
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43 ## where @var{r} is the residual error
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44 ##
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45 ## @example
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46 ## @var{r} = @var{b} - @var{A} * @var{x}
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47 ## @end example
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48 ##
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49 ## As the matrix @var{s} is symmetric indefinite it can be factorized with
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50 ## @code{lu}, and the minimum norm solution can therefore be found without the
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51 ## need for a @code{qr} factorization. As the residual error will be
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52 ## @code{zeros (@var{m}, @var{m})} for underdetermined problems, and example
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53 ## can be
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54 ##
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55 ## @example
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56 ## @group
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57 ## m = 11; n = 10; mn = max (m, n);
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58 ## A = spdiags ([ones(mn,1), 10*ones(mn,1), -ones(mn,1)],
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59 ## [-1, 0, 1], m, n);
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60 ## x0 = A \ ones (m,1);
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61 ## s = spaugment (A);
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62 ## [L, U, P, Q] = lu (s);
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63 ## x1 = Q * (U \ (L \ (P * [ones(m,1); zeros(n,1)])));
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64 ## x1 = x1(end - n + 1 : end);
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65 ## @end group
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66 ## @end example
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67 ##
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68 ## To find the solution of an overdetermined problem needs an estimate of the
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69 ## residual error @var{r} and so it is more complex to formulate a minimum norm
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70 ## solution using the @code{spaugment} function.
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71 ##
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72 ## In general the left division operator is more stable and faster than using
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73 ## the @code{spaugment} function.
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74 ## @seealso{mldivide}
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75 ## @end deftypefn
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76
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77 function s = spaugment (A, c)
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78 if (nargin < 2)
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79 if (issparse (A))
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80 c = max (max (abs (A))) / 1000;
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81 else
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82 if (ndims (A) != 2)
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83 error ("spaugment: expecting 2-dimenisional matrix");
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84 else
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85 c = max (abs (A(:))) / 1000;
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86 endif
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87 endif
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88 elseif (! isscalar (c))
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89 error ("spaugment: C must be a scalar");
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90 endif
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91
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92 [m, n] = size (A);
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93 s = [ c * speye(m, m), A; A', sparse(n, n)];
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94 endfunction
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95
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96
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97 %!testif HAVE_UMFPACK
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98 %! m = 11; n = 10; mn = max (m ,n);
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99 %! A = spdiags ([ones(mn,1), 10*ones(mn,1), -ones(mn,1)],[-1,0,1], m, n);
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100 %! x0 = A \ ones (m,1);
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101 %! s = spaugment (A);
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102 %! [L, U, P, Q] = lu (s);
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103 %! x1 = Q * (U \ (L \ (P * [ones(m,1); zeros(n,1)])));
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104 %! x1 = x1(end - n + 1 : end);
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105 %! assert (x1, x0, 1e-6);
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106